Trimming procedure and code reuse for highly precise dc-dc converters

Abstract

A voltage conversion system provides gain and offset trimming for generating a controlled output voltage. The system includes a digital-to-analog converter (DAC) that generates a reference voltage based on an input code, and a voltage converter that converts an input voltage to an output voltage based on the reference voltage. A first adjustable reference circuit provides a first reference signal to the DAC and a second adjustable reference circuit provides a second reference signal to the DAC. Control circuitry adjusts the first adjustable reference circuit to perform gain trimming of the output voltage and adjusts the second adjustable reference circuit to perform offset trimming of the output voltage. A calibration procedure includes adjusting for both gain and offset, with a two-step approach for positive offset conditions—first incrementing the input code to create a negative offset, then performing offset trimming.

1 . A voltage conversion system with trimming capability, comprising:
 a digital-to-analog converter (DAC) configured to convert an input code to a reference voltage;   a voltage converter configured to generate an output voltage in response to an input voltage and the reference voltage;   a first adjustable reference circuit coupled to the DAC and configured to provide a first reference signal to the DAC;   a second adjustable reference circuit coupled to the DAC and configured to provide a second reference signal to the DAC; and   control circuitry configured to:
 adjust the first adjustable reference circuit to perform gain trimming of the output voltage; and 
 adjust the second adjustable reference circuit to perform offset trimming of the output voltage. 
   
     
     
         2 . The voltage conversion system of  claim 1 , wherein the first adjustable reference circuit comprises a resistive network with multiple selectable taps. 
     
     
         3 . The voltage conversion system of  claim 2 , wherein the control circuitry sets a resistance value for adjusting the first adjustable reference circuit by selecting among the multiple selectable taps. 
     
     
         4 . The voltage conversion system of  claim 1 , wherein the second adjustable reference circuit comprises a resistive network with multiple selectable taps. 
     
     
         5 . The voltage conversion system of  claim 1 , wherein the DAC comprises a resistive ladder network coupled to the second reference signal. 
     
     
         6 . The voltage conversion system of  claim 1 , wherein the control circuitry is configured to perform a calibration procedure by:
 adjusting the first adjustable reference circuit until the output voltage reaches a desired voltage range; and   adjusting the second adjustable reference circuit until the output voltage reaches a desired offset.   
     
     
         7 . The voltage conversion system of  claim 6 , wherein the calibration procedure further comprises, when the output voltage reaches a positive offset relative to a given offset:
 adjusting the input code to create a negative offset; and   adjusting the second adjustable reference circuit until the output voltage reaches the desired offset.   
     
     
         8 . The voltage conversion system of  claim 1 , further comprising a feedback circuit coupled between an output of the voltage converter and the voltage converter, wherein the feedback circuit generates a feedback signal in response to the output voltage and the reference voltage. 
     
     
         9 . The voltage conversion system of  claim 1 , wherein the first adjustable reference circuit is adjustable to provide multiple operating ranges for the output voltage. 
     
     
         10 . The voltage conversion system of  claim 1 , further comprising a buffer circuit coupled between the DAC and the voltage converter, the buffer circuit configured to buffer the reference voltage. 
     
     
         11 . A method for trimming voltage output in a voltage conversion system, comprising:
 generating a first reference signal;   generating a second reference signal in response to the first reference signal;   generating a digital-to-analog converter (DAC) output based on an input code and the second reference signal;   converting an input voltage to an output voltage based on the DAC output;   adjusting the first reference signal to perform gain trimming of the output voltage; and   adjusting the second reference signal to perform offset trimming of the output voltage.   
     
     
         12 . The method of  claim 11 , wherein adjusting the first reference signal to perform gain trimming comprises selecting a tap point in a first resistive network. 
     
     
         13 . The method of  claim 11 , wherein adjusting the second reference signal to perform offset trimming comprises selecting a tap point in a second resistive network. 
     
     
         14 . The method of  claim 11 , further comprising:
 determining whether the output voltage has a desired voltage range; and   adjusting the first reference signal until the output voltage is within the desired voltage range.   
     
     
         15 . The method of  claim 11 , further comprising:
 determining whether the output voltage has a negative offset or a positive offset relative to a desired offset;   when the output voltage has a negative offset, adjusting the second reference signal until the output voltage reaches the desired offset; and   when the output voltage has a positive offset:
 adjusting the input code to create a negative offset; and 
 adjusting the second reference signal until the output voltage reaches the desired offset. 
   
     
     
         16 . The method of  claim 11 , further comprising generating a feedback signal based on the output voltage and providing the feedback signal to control said converting the input voltage to the output voltage. 
     
     
         17 . The method of  claim 11 , further comprising storing multiple settings for the first reference signal to enable selection between multiple operating ranges for the output voltage. 
     
     
         18 . The method of  claim 11 , wherein generating the DAC output comprises using a resistive ladder network coupled to the second reference signal. 
     
     
         19 . The method of  claim 11 , further comprising buffering the DAC output before using it in said converting the input voltage to the output voltage. 
     
     
         20 . The method of  claim 11 , further comprising performing a calibration procedure comprising the gain trimming and the offset trimming to achieve a desired output voltage characteristic.